text: // Licensed to the Apache Software Foundation (ASF) under one
  // or more contributor license agreements.  See the NOTICE file
  // distributed with this work for additional information
  // regarding copyright ownership.  The ASF licenses this file
  // to you under the Apache License, Version 2.0 (the
  // "License"); you may not use this file except in compliance
  // with the License.  You may obtain a copy of the License at
  //
  //   http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing,
  // software distributed under the License is distributed on an
  // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  // KIND, either express or implied.  See the License for the
  // specific language governing permissions and limitations
  // under the License.
  
  #pragma once
  
  #include <algorithm>
  
  #include "arrow/util/bit-util.h"
  
  namespace arrow {
  namespace internal {
  
  struct BitmapWordAlignParams {
    int64_t leading_bits;
    int64_t trailing_bits;
    int64_t trailing_bit_offset;
    const uint8_t* aligned_start;
    int64_t aligned_bits;
    int64_t aligned_words;
  };
  
  // Compute parameters for accessing a bitmap using aligned word instructions.
  // The returned parameters describe:
  // - a leading area of size `leading_bits` before the aligned words
  // - a word-aligned area of size `aligned_bits`
  // - a trailing area of size `trailing_bits` after the aligned words
  template <uint64_t ALIGN_IN_BYTES>
  inline BitmapWordAlignParams BitmapWordAlign(const uint8_t* data, int64_t bit_offset,
                                               int64_t length) {
    static_assert(BitUtil::IsPowerOf2(ALIGN_IN_BYTES),
                  "ALIGN_IN_BYTES should be a positive power of two");
    constexpr uint64_t ALIGN_IN_BITS = ALIGN_IN_BYTES * 8;
  
    BitmapWordAlignParams p;
  
    // Compute a "bit address" that we can align up to ALIGN_IN_BITS.
    // We don't care about losing the upper bits since we are only interested in the
    // difference between both addresses.
    const uint64_t bit_addr =
        reinterpret_cast<size_t>(data) * 8 + static_cast<uint64_t>(bit_offset);
    const uint64_t aligned_bit_addr = BitUtil::RoundUpToPowerOf2(bit_addr, ALIGN_IN_BITS);
  
    p.leading_bits = std::min<int64_t>(length, aligned_bit_addr - bit_addr);
    p.aligned_words = (length - p.leading_bits) / ALIGN_IN_BITS;
    p.aligned_bits = p.aligned_words * ALIGN_IN_BITS;
    p.trailing_bits = length - p.leading_bits - p.aligned_bits;
    p.trailing_bit_offset = bit_offset + p.leading_bits + p.aligned_bits;
  
    p.aligned_start = data + (bit_offset + p.leading_bits) / 8;
    return p;
  }
  
  }  // namespace internal
  }  // namespace arrow
  